Article: BHP vs HP vs kW and other power conversions

[Billzilla]

Just stirring ...

[oldcorollas]

True, but then again a F1 car beats basically anything on a xxx/weight ratio.

this thread is funny... lucky we haven't had 11tybillion like it before

Hiro. even seen a drag car? i would contend that there are MANY cars with higher power or torque to weight ratio than an F1 car. however... most of those won't turn corners ...

[Hiro]

this thread is funny... lucky we haven't had 11tybillion like it before

Hiro. even seen a drag car? i would contend that there are MANY cars with higher power or torque to weight ratio than an F1 car. however... most of those won't turn corners ...

Yes, I am aware of drag cars, and their potential. Hence the "basically" term (and therefore exceptions), compared to "absolutely". And I never said that F1 cars had a huge torque/weight ratio (they don't, it's only about 25% more than a V8 Supercar). Power/weight ratio is greater than just about anything on 4 wheels apart from drag cars though (1HP/kg, essentially, or go back to the turbo 80s ones with about 2HP/kg) And your comment about ability to turn corners is true, I consider F1 cars race cars, and dragsters as purely life support for an engine.

[oldcorollas]

LOL and what great engines they are!!!

[o_man_ra23]

Perhaps.

But if the first car has 3 gears and the second one has 6, the theoretical differences might be reduced.

The rest of your post is good, but if you re-read mine, i stated

2 cars making the same amount of torque, same weight, and perfect gearing for the motor

and thus removed the hypothetical difference between gearings.

BillZilla... that picture is GOLD!! +rep for you, i just love that sorta shit stirring

Cheers, Owen

[river]

Hi,

Don't get too hung up about engine torque. The torque that really matters is the maximum torque imparted to the ground by the tyres .

The torque and horsepower peaks of an engine do not necessarily occur simultaneously. Considering only the torque peak neglects the potential torque multiplication offered by the transmission, final drive ratio and tyre diameter. It's the torque applied by the tyres to the ground that actually accelerates a car, not the torque generated by the engine.

Horsepower, being the rate at which torque is produced, is an indicator of how much "potential" torque multiplication is available. In other words, horsepower describes how much engine rpm can be traded for tyre torque. The word "potential" is important here. If a car is not geared properly, it will be unable to take full advantage of the engine's horsepower.

A car running at peak power at a given vehicle speed is delivering the maximum possible torque to the tyres, even though the engine may not be spinning at its torque peak.

seeyuzz
river

[Norbie]

HP sells cars, torque wins races. That's why nearly all race cars have diesel engines.

Oh wait...

[kingmick]

HP sells cars, torque wins races. That's why nearly all race cars have diesel engines.

Oh wait...

no but thats why the fastest tin tops in australia run CHEVS. nothing like having 580-620fp of torque on tap from 3800rpm or so.
Unless you have 5 times the budget of a CHEV powered car you want beat the chev with a turbo car ciruit racing in australia. besides the fact that if you want to play tactics you just back the turbo cars down with your chev mid corner and you will have 4 car lengths on them coming out of the corner!lmao it works a treat if your having a slow day.

[chris davey]

I have a question.

We are saying that torque at the engine is not useful (much like flywheel hp) and that torque at the wheels is what is important.

When on a dyno it measures tractive force which is different from torque AFAIK yet on dynojet dynos in the US they always have the torque curve in ft/lbs. As their dynos also read higher in hp it is easy to see if the engine is a torquey one or not if the hp is about the same as the torque ie. 500rwhp 500ft/lbs torque.

So as we are saying that torque at the wheels is most important why don’t our dynos measure this so that you can tune for maximum torque? (or area under the curve)

[SL666]

Dyno dynamics dynos (all retarder types) do measure tractive effort, which will give you an indication of torque when graphed with RPM.

[chris davey]

So is this the same as what dynojets do then?

So I know what a torquey engine should produce compared to hp numbers but what about kw to nm?

Or should you not bother with that and just work on getting the most area under the torque curve?

[SL666]

not really..

im sorry im sick at the moment so im a bit spacial.. - bear with me..

A dyno jet dyno does not have a retarder, or any way to hold load on an engine, it only measures the speed of the known mass of the big-ass roller, and then extrapolates the amount of force per sample time required to accelerate the roller.. and indeed wheelspin here can infact spike the figures when the roller catches to the wheels (because of the rotating mass of the driveline etc)

a DD dyno indeed measures the force/work etc acting apon the roller at any one point, and then plots the force/work against the speed of the rollers.

they just measure things differently, i guess the dynojet is much more like estimating HP from MPH..

for drag racing.. you want the maximum amount of HP within the RPM that your car is operating in during the run.. now whether or not its better to have say

assuming a used RPM band of 6-7000 rpm..
200kw at 6000 and 200kw at 7000
195kw at 6000 and 205kw at 7000
or 170kw at 6000 and 230kw at 7000
is best? i don't know.. i guess it would be better to have the 230 at 7000? because the car would be pushing more air as it gets faster?

or maybe the 200kw at 6000 would be better if your car is going to be against the stall for a longer period of time at that?

[RONA]

HP sells cars, torque wins races. That's why nearly all race cars have diesel engines.

Oh wait...

Lol but the New Audi in the Lemans Prototype series runs them and alas is still winning.

[Lonewolf]

Great contribution Strad...

If you, or anyone, has the time to do some more research ...
I'd be keen to see a reliable flywheel to rearwheel conversion formula & vice versa.

From what I can see around, most people work on rearwheel being somewhere between 70% to 80% of the flywheel power.

I know that this gets complex when you look at various drivetrain configurations, etc, but surely their could be some reliable way of doing this, that would help to resolve a few debates.

Yeah, you can accurately work it out, it involves a run on an engine dyno, and a run on an inertial chassis dyno. Both would need to be set up properly, by people who know their stuff, done with identical conditions, and you would end up with a way of telling drivetrain losses on your vehicle. Thats probably the closest reasonable way to get something resembling absolute power readings at the wheels and flywheel short of doing the same thing in a lab with controlled conditions. You shouldn't need to do that too often, unless your seeking to reduce drivetrain losses

Unfortunately this is going to vary if you used a braked chassis dyno (which is what most are) as they vary alot between different dyno's, and hell even on the same dyno if the operator isn't competantor, and even if they are, the flaws of a braked chassis dyno mean that the readings will only be meaningful if you use that dyno constantly, as it wont give an absolute reading, but being fairly repeatable will show relative differences up, which is what keeps most people happy. The reason people use 20% or 30% drivetrain losses is that it doesnt matter for the average person, as long as the same number is being used constantly

[o_man_ra23]

Lonewolf,
I think you missed the bit where 3T-GTE asked for a conversion formula. As back to back runs on an engine dyno and a vehicle dyno are not in any way classed as a conversion formula, i dont think that you gave him the answer he was after. But you are correct that what you have said is the way to do this test. Just a pity that its already been mentioned in this thread.

Cheers, Owen